How should I practice Topmost Accessible Nodes?

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Topmost Accessible Nodes

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Problem statement

A hierarchy contains teams, folders, and files. It is represented as a forest of nodes.

nodeIds[i] is the unique ID of node i.
parent[i] is the parent index, or -1 when node i is a root.
readableUsers[i] lists the users with direct read access to node i.

Direct access to a node also grants access to every descendant. For userId, return the smallest covering set of nodes: whenever the user has direct access to a node, include that node and do not include any accessible descendant beneath it.

Return selected node IDs in forest preorder. Roots and siblings follow their order in the input arrays.

Function

fewestAccessibleNodes(nodeIds: String[], parent: int[], readableUsers: String[][], userId: String) → String[]

Examples

Example 1

nodeIds = ["Team1","Folder1","File1","File2","Folder2","Folder3"]parent = [-1,0,1,1,0,4]readableUsers = [[],["A"],["A"],[],[],["A"]]userId = "A"return = ["Folder1","Folder3"]

Folder1 covers both files beneath it, so File1 is redundant. Folder3 is in another branch and is also required.

Example 2

nodeIds = ["Team1","Folder1","File1","Folder2"]parent = [-1,0,1,0]readableUsers = [["A"],["A"],["A"],[]]userId = "A"return = ["Team1"]

Access at the root covers every descendant, so it is the only selected node.

Example 3

nodeIds = ["RootA","LeafA","RootB","LeafB"]parent = [-1,0,-1,2]readableUsers = [[],["U"],[],["U"]]userId = "U"return = ["LeafA","LeafB"]

Neither root grants access, so each directly readable leaf must be returned.

Constraints

1 <= nodeIds.length <= 200000.
nodeIds.length == parent.length == readableUsers.length.
Node IDs are unique.
For every non-root node i, 0 <= parent[i] < i.
The total number of direct user entries is at most 200000.